with both increased smoking behaviors (Schaap and Kunst 2009; Tjora et al. 2011) and anxiety (Kessler et al. 2005). Inhibitors,research,lifescience,medical Despite the significant Inhibitors,research,lifescience,medical health impacts arising from the comorbidity between smoking and anxiety, the biological mechanisms underpinning this association have received less investigation than for other psychiatric disorders. The relationship between smoking and anxiety is complex as evidence supports that cigarette smoke can reduce anxiety in some smokers (see review Morissette et al. 2007). In addition, smokers often report increased anxiety post smoking

cessation, although recent data conflict with this finding (Bolam et al. 2011; McDermott et al. Inhibitors,research,lifescience,medical 2013). There is also significant heritability in both anxiety expression and smoking behaviors. Recent advances in understanding the etiology of mood and anxiety disorders support a key role for neurotransmitter systems, the immune system, oxidative and nitrogen stress (O&NS), mitochondrial dysfunction, neurotrophins (NTs) and neurogenesis, and epigenetic effects in pathogenesis (Berk et al. 2011; Moylan et al. 2012b). All Inhibitors,research,lifescience,medical of these systems are affected by exposure to cigarette smoke. This review critically examines and summarizes the literature that has explored how cigarette smoking may increase the likelihood of developing increased anxiety and anxiety disorders. In this review, we focus on relevant biological mechanisms Dipeptidyl peptidase (e.g., neurotransmitter systems, inflammation, oxidative and nitrosative stress, mitochondrial dysfunction, dysregulation of NTs and neurogenesis, and epigenetic effects) that potentially mediate how smoking may influence anxiety symptoms. Extensive literature has explored numerous psychological and social contributors to a relationship between anxiety and cigarette smoking. Readers interested in these pathways should consult the numerous excellent reviews available (Zvolensky et al. 2005; Morissette et al. 2007; Ameringer and Leventhal 2010).